Thermal integrator



May 13, 1958 P. A. NOXON THERMAL INTEGRATOR Filed Dec. 1a. 1953 2 2 un il THERMAL INTEGRATOR Paul A. Noxon, Tenafly, N. .l., assignor to Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application December 18, 1953, Serial No. 399,106

5 Claims. (Cl. 323--69) This invention relates generally to integrators and more particularly to electrical circuits for performing integration.

Copending application Serial No. 90,236, now U. S. Patent No. 2,724,418, granted July 10, 1956, to Alfred Bennett and John C. Owen, and assigned to Bendix Aviation Corporation, describes an integrating circuit com prised of a preamplifier for receiving and amplifying a signal, a discriminator for detecting the phase of the signal and developing a corresponding output, a thermal time delay device for receiving the discriminator output and developing corresponding outputs after a delayed interval of time, and a feedback for degeneratively feeding the delayed output back to the input. The delayed output corresponds to an integral of the input.

While the above circuit worked well, it did have certain limitations. One limitation was that the total output limit under a given condition was proportional to the output of the discriminator. However, in systems where constant operating limits of a large signal value were frequently required, the discriminator became saturated and developed a substantially constant control output. The output of the integrator at this time did not correspond to the rate of change of the input but was a step function having a time rate dependent upon the characteristics of the thermal time delay device.

An object of the present invention, therefore, is to States Patent provide a novel device for providing an output corresponding to an integral of the input although the input may. have a relatively large signal value.

Another object of the invention is to provide a normally balanced network whose two adjacent arms become unbalanced in response to an input signal and although one arm becomes unbalanced more rapidly than the other, the two arms will again reach a balanced condition as the input signal becomes constant.

The foregoing and other objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawing wherein one embodiment of the invention is illustrated by way of example. it is to be expressly understood, however, that the drawing is for the purpose of illustration and description only, and is not intended as a definition of the limits of the invention.

The single figure in the single sheet of drawing illustrates a complete schematic wiring diagram of the novel circuit for developing an output proportional to an integral of the input.

The novel circuit of the present invention is comprised generally of a signal source 5, a' coupling transformer 6, a preamplifier 7, a discriminator 3, a pair of thermal time delay devices 9 and 10, a feedback transformer 11, and an output 12.

The signal source 5 may be a conventional inductive signal generating device in which a rotor 15 is movable relative to the stator 17 to produce a control signal. This signal is impressed across a coupling transformer 6 and applied to preamplifier 7 where the signal is given two stages of amplification.

Preamplifier may be a conventional dual triode whose output is applied across a coupling transformer 25 to the grids 27 and 28 of a twin triode 8 constituting the discriminator.

In discriminator 8, plate 31 is connected through series connected heater windings 33 and 34 of thermal time delay devices 9 and 10 and plate 35 through heater windings 36 and 3'7 to a source of alternating current. While the voltages on the plates are in phase, the voltages on the grids resulting from a signal coupled across transformer 25 are in opposition. Therefore, only the discriminator section having its grid and plate in phase will conduct current through the series connected heater elements in thermal time delay devices 9 and 10.

Thermal time delay devices 9 and 10 may be of the type described in U. S. Patent No. 2,463,805, issued March 8, 1949, to Polye et .al. wherein two heater-resistance sections are enclosed in an evacuated envelope. Each section is comprised of a heater winding surrounded by a quartz glass insulator around which a resistance winding is placed. A current differential in the heater windings of the two sections of a thermal time delay device results in a temperature change in the quartz insulators and a corresponding change in the relative resistance values of the resistor windings on the insulators. The time constant of the device, represented by the time required for a change in current in the heater windings to appear as a change in output of the tube, may be varied by changing the insulation in the manufacturing of the tube.

Thermal time delay devices 9 and 1t) herein are so chosen as to have substantially different time constants but substantially the same output impedances. Their resistance windings are connected to form a bridge network having four arms: resistance windings 41, 42, 43 and 44. Excitation is applied by a suitable source of alternating current including a transformer 45 connected across the diagonal formed by terminals 46, 4'7 and the bridge output is taken from terminals 48, 49 and applied across a feedback transformer 11 to be added degeneratively to the input signal at transformer 6. The transformer 45 may be of a conventional type having a split secondary winding 50 grounded at 51 and connected across the input to the thermal time delay device It) hav ing the slower time constant so that the output of the slower thermal time delay tube at 12 relative to ground provides the output of the circuit. Normally the bridge is balanced, and discriminator 3 is biased so that the heaters of the thermal time delay devices are normally heated to the midpoint of their usual temperature. Since the two thermal time delay devices have substantially the same irnpedances and temperature coefficients, the amount of static unbalance will be substantially the same in the two devices provided sufficient time has elapsed for transients to have died out.

In operation, a signal from a suitable source, such as inductive device 5, is coupled across transformer 6 to preamplifier 7. After two stages of amplification in preamplifier 7, the signal is applied across coupling transformer 25 to discriminator 8. Depending upon the phase of the signal, one triode section of the discriminator will conduct more current and the other section less. Different currents will then flow through the corresponding serially connected upper windings 33 and 34 of thermal time delay tubes 9 and 10 than through lower windings 36 and 37. The heat generated in these windings will change the resistance value of the resistance windings which are in heat exchange relationship with them.

During a condition of change of input signal, the thermal time delay device 9 having the faster time constant 3 will experience a change in resistance earlier than the other device however, there will be a difierence in output of the two tubes which is a function of the rate of change of input. Feeding this unbalance back to the input in degenerative fashion will regulate the rate of change of input to, the thermal time delay devices.

When a signal input of constant value causes a saturation of the discriminator to be reached, the unbalance of one unit of each of the two tubes will progressively change with time; however, a constant difierence will be maintained. This change will continue but the slower heating tube is also being heated and tends to rebalance the bridge as the saturation level of the thermal time delay device is reached.

Although only a single embodiment of the present invention has been illustrated and described in detail, it is to. be expressly understood that the invention is not limited thereto. Various changes can be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as will now be understood by those skilled in the art. For a definition of the limits of the invention, reference will be had primarily to the appended claims.

I claim:

1. A circuit for obtaining the linear function of the rate of change of energy input comprising a Wheatstone bridge capable of an energy output when unbalanced, a means responsive to the energy input to unbalance adjacent arms of said bridge including means for delaying for an. interval of time the unbalancing of said bridge so that at a time intervalafter the energy input one arm of saidbridge unbalances and after afurther interval an adjacent arm of said bridge unbalances, a means to feed the output of the bridge back to the input and a means for obtaining as an output a portion of the output as the signal corresponding to the rate of change of input.

2. A circuit for obtaining the signal corresponding to the linear function of the rate of change for an energy. input comprising a plurality of means capable offa balanced and an unbalanced condition for releasing energy when in an unbalanced condition, a means responsive to the energy input for unbalancing said first named means, a means for delaying the unbalancing of said first named means so that at an interval after the energy input one of said first named means becomes unbalanced and ata later interval another is unbalanced, means for feeding the energy released back degeneratively to said energy input, and means for obtaining a portion of the energy of said latter unbalanced means as a signal, the latter signal being the linear function of the rate of change of the energy input.

3. A device of the class described comprising an input means for receiving an input signal of reversible sense, a-normally balanced bridge network capable of an energy output when unbalanced, first means for heating two adjacent arms of said network to unbalance the bridge network in one sense, second means for heating opposite adjacent arms of said network to unbalance .the bridge network in an opposite sense, said heating means being operative independent of said bridge network, and means responsive to the sense of the input signal to selectively energize said first and second heating means to unbalance the bridge network in a sense dependent upon the sense of the input signal.

4-. A device of the class described comprising, an input means for receiving an input signal of reversible sense, a pair of thermal time delay devices including in eachdevicea pain of resistance elements and independently operable means for selectively heating the resistance elements,,the resistance elements of one time delay. device having, difierent time constants from the resistance elements. of the other of said time delay devices and said resistance elements having substantially the same impedance, the resistance elements of the said devices being operatively connected-in a normally balanced bridge net work capable of an energy output when unbalanced, means responsive to the input signal of one sense to selectively-energize the-heating means of said devices-to vary the resistance of one of the elements of each. of said devices. to unbalance the bridge network in one sense, and said selective, means responsive to the input signal of an opposite: sense to selectively energize the heating means of said devicesto vary the resistance of the. other of the-elements of each of: said devices to unbalance the bridge, network in an opposite. sense.

5; The combination defined by claim 4, including means to feed the output of the bridge network to the input: in opposition to: the input signal, and other means for obtaining. anoutput signal'from oneof the time delay devices.

Rieber Dec. 31, 1935 Davis Nov. 4, 1952 

